Coho salmon (O. kisutch) reared in a freshwater pond were transported by ship from Wakayama Prefecture to Otsuchi Bay, Iwate Prefecture, in November 1979. The fish were immediately transferred to a pen for marine culture in seawater, and mortality was observed. The cumulative mortality after ten days was approximately 80 percent. On examination of the diseased fish, Aeromonas salmonicida was considered to be the causative agent of the extensive mortality, but a mixed infection with Vibrio anguillarum was observed in a few cases. We tried to determine the origin of this disease. A. salmonicida was isolated from freshwater cultured coho salmon remaining in Wakayama, and relatively high agglutination titer for the organism was detected in their sera. It was concluded from this that A. salmonicida is probably carried by freshwater cultured fish and can be transmitted during the transport. The results of this study suggest that it needs to control furunculosis throughout the stage of freshwater culture and to reduce physiological stress as much as posible during transport of salmon to the marine culture site.
Several milkfish (Chanos chanos) juveniles polycultured with the Indian prawn (Penaeus indicus) in earthen ponds at the Leganes Station of the Aquaculture Department, SEAFDEC, Philippines, manifested eye abnormalities. Signs observed varied from unilateral and bilateral opaque eye coverings/eye balls, exophthalmia and hemorrhagic eyes. A vibrio was predominantly isolated from the opaque eye coverings and eye balls, and it was proved pathogenic to milkfish, Japanese eel (Anguilla japonica) and mouse by injection experiments. The opaqueness of eye coverings of milkfish was likewise reproduced by a combination of injury and contact with the pathogen. The bacterium, though seemed closely related to Vibrio parahaemolyticus or V. alginolyticus, was not identified to any known Vibrio species.
Vibrio anguillarum produced heat labile(70°C, 10 min) exotoxin lethal to goldfish, Japanese eel, ayu and mouse when injected. The extracellular products(ECP)from cellophane plate cultures(nutrient agar or BHI agar)at 20°Cor 25°Cfor 18-36 h were toxic, but not in 24 h BHI broth culture at 25°C. No lethal endotoxin was detected in filtrate of sonicated cells or heated cells obtained from cellophane plate culture.The lethal dose of the crude ECP from a high virulent strain was approximately 15μg protein/g fish(goldfish). Proteolytic activity of ECP, which was measured by using azocasein as reaction substrate, was re-cognized to coexist together with lethal toxicity. When virulent strains were compared with low virulent strains, the production of the lethal exotoxin and protease well correlated with the virulence.
A description is given of Benedenia hoshinai sp. nov.(Monogenea, Capsalidae)on the body surface and fins of the Japanese striped knifejaw, Oplegnathus fasciatus(Japanese name“ishi-dai”), cultured in Nagasaki Prefecture. The new species is separated from previously known species of the genus by the shape of the opisthohaptoral hard parts and/or of the male copulatory organ.
Since 1979, occurrences of a new disease in cultured eels have been observed from late autumn to spring in Kagoshima and other prefectures. This disease has been tentatively called head ulcer disease because of its unique sign of ulcerative lesions formed on the head part of affected eels. Bacterial isolations were made from the ulcerative lesions, liver and kidney of the diseased eels (Anguilla japonica) in Tokushima and Shizuoka Prefectures, and at Hiroshima University from 1981 to 1983. A bacterium, which formed small colonies on nutrient agar without pigment production after 48-72 h incubation at 20°C or 25°C, was isolated purely or dominantly from almost all the fish examined. From the morphological, biochemical, serological and genetical(GC value)properties, the organism was classified as atypical Aeromonas salmonicida. The LD50 of an isolate to Japanese eel was revealed less than 102 CUF/100 g fish by intramuscular injection, and subcutaneous injections into the head or nasal part of eels reproduced ulcerative lesions and exophthalmus. The mortality of artificially infected eels varied with ambient water temperature:10°C-30%, 15 and 20°C-100%, 25°C-70%, 30°C-0%.
In 1982, a bacterial disease occurred among cultured eel at the Fisheries Laboratory, University of Tokyo, in Shizuoka Prefecture. The typical symptom of this disease was a swollen head. Several fish were killed every day, and the total mortality by this disease was about 50-60%. The bacteria isolated from the diseased fish were Gram-negative and non-motile. Catalase, cytochrome oxidase, gelatinase, esculin hydrolysis, VP reaction and growth at 37°C were negative. Carbohydrate utilization was fermentative. Citrate utilization and indole production were positive. The organisms showed different reactions at maltose and mannitol utilization, and ONPG test. And one of the organisms (maltose-negative, mannitol-positive, and ONPG test-negative) has the same characteristics of the causative agent from ulcerative disease in goldfish. The present isolates showed pathogenicity for eel by the intraperitoneal injection.
An ulcer disease occurred with high mortalities among cultured eels in various ponds in Kagoshima Prefecture between October 1982 and March 1983. The diseased eels were associated with extensive ulcerative lesions on the head and body. On the basis of the bacteriological characteristics of the isolates from diseased eels were classified into atypical Aeromonas salmonicida; the characteristics of the isolates differed from those of the subspecies of salmonicida, achromogenes, and masoucida. The biochemical characteristics of the isolates, as far as we tested, did not coincide with those of typical A. salmonicida isolated from ulcerative diseases of minnows, Phoxinus phoxinus, goldfish, Carassius auratus, Atlantic salmon, Salmo salar, and carp, Cyprinus carpio. A common antigen was observed in our isolate, A. salmonicida subspecies salmonicida, A. salmonicida subspecies masoucida, and an atypical A. salmonicida from goldfish with ulcer disease. However, the antigen of the isolate was partially different from those of A. salmonicida suspecies masoucida and atypical A. salmonicida. Isolates had a strong autoaggregating tendency and an additional surface “A” layer.
From September to October, 1983, mass mortality of the anchovy Engraulis japonica occurred in the Sea of Iyo (part of Inland Sea; “Iyo-nada”), north of Sadamisaki Peninsula, Ehime Prefecture. Dead and dying fish were seen floating about thirty kilometers along the coast, and the number was estimated to be more than eighty-seven thouthand during that period. The common symptoms were gauntness and anemia. Out of 155 anchovies, 153 (99%) had a gill monogenean Pseudanthocotyloides sp. (Mazocraeidae), compared with much lower prevalence (0-17%) in the anchovy collected from several other localities in the prefecture. No bacterial infection was thought to be involved, and no extraordinary changes in the water quality were detected during that time. It is concluded that the mortality was caused by the monogenean.